A plasma processing apparatus for performing a film forming process, an etching process or the like by using a plasma has been used in manufacturing various semiconductor devices made of, e.g., silicon or compound semiconductors, an FPD (flat panel display) such as an LCD (liquid crystal display), and the like. In such a plasma processing apparatus, a member made of a dielectric material such as quartz or the like is widely used as a chamber component part constituting a plasma generation space. For example, in a microwave-excited plasma processing apparatus for generating a plasma by introducing a microwave into a processing chamber by a planar antenna having a plurality of slots, the microwave propagated through a waveguide is introduced into the chamber via the planar antenna and a microwave transmitting plate made of quartz and then reacts with a processing gas, thereby generating a high-density plasma (see, e.g., Japanese Patent Laid-open Application No. 2000-294550 (FIG. 3 for example)).
Meanwhile, in the manufacture of various semiconductor devices or products such as an FPD and the like, there is set a influence value for the number of particles allowed for a product management (allowable number of particles). Therefore, reducing the number of particles is important for the improvement of a product yield. However, in a silicon nitride film forming process of nitriding silicon on a surface of a target substrate by using the microwave-excited plasma processing apparatus configured as described above, particles in excess of the influence value are generated if the number of processed sheets exceeds 1000, for example. And further, as the number of processed sheets increases, the number of particles also increases. The number of particles particularly increases after a long period of idle time (i.e., after the apparatus is not operated for a long time) has elapsed. Further, a particle generation state varies depending on plasma processing conditions. To be specific, particles are apt to be generated when a plasma nitriding process is repeatedly performed under low pressure and high power conditions.
When the plasma nitriding process is repeatedly performed, the number of particles gradually increases and thus a production yield deteriorates as described above. Therefore, the number of particles needs to be reduced below the reference value (allowable number of particles) during the whole processes, and a measure therefor is required.